High-frequency oscillator



Sept. 16, 1947. R. C. JENSEN ET AL I 2,427,558

HIGH FREQUENCY OSCILLATOR Filed June 24, 1942 I I a 2%.

he'nr Attorney.

Patented Sept. 16, 1947 UNITED STATES PATENT OFFICE HIGH-FREQUENCYOSCILLATOR Richard C. Jensen and James E. Keister, Scotia, N. Y.,assignors to General Electric Company, a corporation of New YorkApplication June24, 1942, Serial No. 448,206

5 Claims. 1

The present invention relates to high frequency electronic apparatus andmore specifically to an improved oscillator for use in a range ofwavelengths between a few meters and a few centimeters.

At wavelengths within the band specified, conventional lumped circuitarrangements for generating oscillations become usable only withdifficulty because of the fact that the conductors employed to link thevarious circuit elements'provide an appreciable and uncontrollable partof the total circuit impedance. For this reason various arrangementsemploying transmission line sections and resonant cavities in place ofconventional tuned circuits have been devised in an effort to circumventthe difliculties referred to. In most cases, however, the arrangementsproposed are complicated and costly to construct and are not readilyadjusted to a desired condition of operation.

It is an object of the present invention to provide an improved highfrequency oscillator which is characterized by simplicity oforganization and by ease of use.

In a typical embodiment the invention employs three telescoped andradially separated conductors which define concentric space-resonantcavities between them. These are used in combination with an electronictube having its grid coupled to the intermediate conductor and its anodeand cathode coupled respectively to the remaining conductors.Oscillations are sustained by feedback coupling between the two cavitiesin a manner which will be explained more fully at a later point.

The features desired to be protected herein are pointed out withparticularity in the appended claims. The invention itself, togetherwith further objects and advantages thereof, may best be understood byreference to the following description taken in connection with thedrawing, in which Fig. 1 is a sectional View of an oscillator suitablyembodying the invention; Fig. 2 is an enlarged view, partially brokenaway, of certain of the structure of Fig. 1; Fig. 3 is a circuit diagramuseful in explaining the invention, and Fig. 4 is a fragmentary detailof a further part of the structure of Fig. 1.

Referring particularly to Fig. 1, there is shown an oscillator whichcomprises a series of three concentric and mutually telescopedconductors H), II and I2, suitably consisting of brass or copper. At oneend the conductors are secured to a common base M which may be either ofmetal or of insulating material. By virtue of their mutual spacing, theconductors provide, in effect, a pair of concentric transmission linesections each of which, by proper termination, can be made to functionas a tank circuit having a particular resonant frequency. With thisconsideration in mind, the outer conductor pair is provided with amovable short-circuiting device in the form of an annular'metal ring [8which bears two sets of contact fingers '20 and 2| respectively arrangedat its inner and outer peripheries. These contact fingers bearsymmetrically upon the opposed surfaces of the conductors l0 and II sothat these conductors are .effectively directly connected through thering l8. The position of the ring may be adjusted by means of externallyaccessible operating rods 23 and 24 which are associated with the ringso that tuning of the transmission line section in question is possible.A similar tuning device comprising a conductive ring 26 and contactfingers 21 and 28 is provided in connection with the conductors H andI2, and an adjusting rod 30 permits external adjustment of this device.

A coupling loop 32 (see Fig. 4) extends into the cavity formed betweenthe conductors H and I2 and makes it possible to abstract high frequencyenergy from this cavity when it is in excited condition. The loop has aconnection with a conductive tube 33 and a further connection with awire 34 which is concentrically arranged within the tube 33, theelements 33 and 34 forming a coaxial transmission line. The tube 33 issecured to the ring 26 in such fashion as to be movable with it and iscapable of being rotated to vary the linkage of the loop 32 with themagnetic field existing in the cavity between the conductors II and I2.This makes it possible to adjust the loop so as to obtain optimumcoupling effect.

The extremities of the conductors H], H and I2 which are remote from thebase part M are axially offset so as to provide a stepwise arrangementwhich i regressive as one proceeds from the outer conductor 10 towardthe inner conductor 12. This is for the purpose of facilitating thecombination of the conductors with an electronic tube which isillustrated in detail in Fig. 2, and which includes an anode 4|, a grid42 and a cathode 43 arranged in end-to-end relation in the order named.The anode, which is a solid metallic cylinder, is supported from a metaldisk 44 which serves both as an end Wall for the tube and as a terminalfor the anode, and a like disk 46 is provided in connection with thecathode 43. A third disk 43 having a central aperture over which thegrid 42 is affixed extends laterally from the central portion of theenvelope and provides a grid terminal. The three disks M, 46 and 48 areinsulatingly separated by means of glass cylinders 50 and which aresealed to the disks and which provide the lateral wall structure of thetube.

The cathode of the tube includes an emissive disk or cap 53 and aheating arrangement for the disk which is enclosed within a hollowtubular structure 54. The heating arrangement comprises a filamentaryemitter 55 and a concentrating sleeve 55 for directing electrons emittedby the filament against the disk 53 from which the principal dischargeof the tube is to be realized, the elements 55 and 56 being indicated indotted outline. Lead-in conductors 58 associated with the filament 55are sealed in insulatingly spaced relation through a glass bead 59 whichis fused into the end of an outwardly projecting metal eyelet 60, theeyelet being afiixed by welding or otherwise to the surface of the disk45.

The tube 45 is preferably highly evacuated and by virtue of itsconstruction is well adapted to serve as a generator of high frequencyoscillations. In the present case, an oscillating circuit is set up bycoupling the various electrode terminals of the tube to the respectiveconductors H], H and I2 in the manner illustrated.

The anode is coupled to the extremity of the conductor [2 through acylindrical metal member 55 which abuts the anode terminal disk 65 andwhich is separated from the conductor l2 only by a thin layer 5! ofdielectric material, such as mica or glass. By virtue of the capacitybetween the adjacent surfaces of the member 55 and the conductor l2, theanode is, in effect, directly connected to the conductor l2 as far ashigh frequency currents are concerned. It is, however, insulated from itwith respect to unidirectional currents so that the member 55 may beemployed as a terminal conductor for applying positive voltage to theanode. To this end a terminal screw 55 set in an insulating block isprovided at the extremity of the member 55.

The connection between the anode terminal 44 and the conductive member55 is made by means of a threaded stud 65 which is secured to the outersurface of the terminal. With this arrangement the member 65 is enabledto serve not only as a D.-C. terminal connection for the anode but alsoas a means for dissipating the heat generated at the anode duringoperation.

The grid terminal 48 is directly conductively connected to the extremityof the intermediate conductor II through a metal ring 13 having acircular array of spring contact fingers l5 which bear upon the undersurface of the terminal disk 48. With this arrangement the rid isgrounded to the resonant structure.

A somewhat similar arrangement is provided in connection with thecathode terminal 45, which is engaged by spring contact fingers 18mounted upon a metallic ring 19, this ring being secured to a furtherring 80 which rests upon the upper extremity of the conductor ID. Adirect contact between the rings 19 and 80 is prevented by theinterposition of an insulating (e. g., mica) washer 82 which is thinenough to assure effective capacitive couplin between the two rings sothat the cathode terminal is, in effect, connected directly to theconductor II! as far as high frequency currents are concerned. Thescrews 84 by which the ring 19 is held in place are insulated from thering by means of insulating eyelets 85 so that these screw do notconstitute a short-circuiting connection. The arrangement is accordinglysuch that the oathode system as a whole can be given a desired D.-C.bias with respect to the other electrodes of the tube.

It will be noted that the anode terminal 64 is of smaller diameter thanthe grid terminal 48 so that the tube may be readily inserted in theoscillator assembly even with the grid contact ring I3 in place. Thecathode contact ring is is not applied until after the tube is insertedin the assembly.

In the use of the apparatus, potential is applied between the cathodefilament 55 (Fig. 2) and the main body of the cathode structure in suchfashion as to cause bombardment and heating of the emissive cap 55 tooccur. Thereafter positive potential is applied to the anode and anappropriate potential relationship is established between the cathodeand grid by a suitable biasing arrangement (not shown). Under thesecircumstances and assuming proper tuning of the inner and outertransmission line sections (1. e., by proper adjustment of the shortingrings l8 and 26), high frequency oscillations may be developed.

The occurrence of such oscillations depends, of course, upon theassumption that proper resonance conditions are provided by the tuningof the transmission line sections and that suitable feedback existsbetween the anode and grid circuits. Under some conditions such feedbackmay occur solely as a result of the internal plateto-cathode capacity ofthe tube. In most cases, however, it is desirable that this coupling beaugmented in some way, and to this end there is provided in the presentinstance a coupling element which extends between the inner and outerresonant cavities. This element comprises a conductive rod which has ascrew-threaded engagement with the rin l9 and which extends through anopening provided in the ring 13. By appropriate rotation of this rod itsdegree of eX- tension into the space between the conductors H and I2 canbe adjusted to produce a desired feedback relationship, theplate-to-cathode capacity obviously being increased as the rod is movedin an inward direction.

The operation of the oscillator described in the foregoing may befurther explained by reference to the schematic diagram provided in Fig.3. In this figure the parallel combination of condenser H15 andinductance llll may be assumed to represent the transmission linesection provided between the conductors H and [2 in Fig. 1, whereas thecombination of condenser I52 and inductance I03 represents thetransmission line section between conductors ID and II. The condenserrepresents the feedback capacity between the anode 4i and the cathode43' (these elements corresponding to the similarly numbered elements ofFig. 2). This capacitance is provided partly by internal tube capacityand partly by the effect of the coupling element 90 (Fig. l).

It will be understood that the desired tuning of the transmission linesections is accomplished by moving the adjustable rings I8 and 26(Fig. 1) until each transmission line has an effective length close tothat of a quarter wave '(or, alternatively, an odd multiple of quarterwaves) at the operating frequency. As previously indicated, somedetuning from the exact quarter wave value will ordinarily provenecessary with respect to one or both lines in order to obtain desiredphase relationships. The high frequency energy realized during operationof the oscillator may-be coupled to an external circuit, such as anamplifier or a radiating antenna, by means of the coupling loop 32 andits associated conductors 34 and 35.

The D.-.C. provisions for the circuit of Fig. 3 include apotentialsource H which is indicated conventional-1y as a battery having itspositive terminal connected to'the anode 4| and its negative terminalconnected to ground and thus to the grid 42'. Grid bias is obtained by aresistor H3 located in the grid-to-cathode circuit. By-pass condensers II and I 16 which correspond respectively to the dielectric spacers 61and 82 of Fig 1 isolate the D.-C. system from the high frequencycircuits. The absence of choke coils in the oathode and anode circuitsis explained by the fact that all high frequency efiects are confined tothe space resonant cavities enclosed by the transmission line sectionsso that, except for leakage through the dielectric spacers 61 and 82, nohigh frequency currents appear in the anode connection 65 or in theexternal cathode connections. In the event high frequency leakagethrough the spacer Bl proves troublesome it can be readily eliminated bythe use of suitable filtering means such as a quarter-wave filtersection (not shown) associated with the conductor 65.

The arrangement shown in Fig. l is exemplary only, and it is entirelyfeasible and within the scope of the invention to reverse theorientation of the tube 48 so that its cathode terminal is coupled tothe inner conductor l2 while its anode terminal is coupled to the outerconductor I0, the grid terminal being still directly connected to theintermediate conductor ll. Under these circumstances, a somewhatdifferent tuning of the transmission line sections will be necessaryand, of course, appropriate changes must be made in the D.-C.connections. With these alterations oscillations may be expected tooccur on a basis explainable by a diagram such as that of Fig, 3.

It should be noted that the tube shown in Fig. 2

is of a type which is more fully described in U. S.

Patent 2,284,405, granted to E. D. McArthur, May 26, 1942, and assignedto the General Electric Company, corporation of New York.

A further embodiment of which our invention has been found capable isdescribed in A. M. Gurewitsch application, S. N. 452,946, filed July 30,1942, this application being also assigned to the General ElectricCompany.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

1. An oscillator comprising three concentric conductors in telescopedrelation, a first transmission line section being provided by thecombination of the inner conductor and the intermediate conductor and asecond transmission line section being provided by the combination ofthe intermediate conductor and the outer conductor, a rotationallysymmetrical electronic tube having its structure mounted substantiallywholly within the confines of said outer conductor and having its axisof symmetry colinear with the common axis of said conductors, said tubeincluding a planar anode, a planar grid and a planar cathode mounted inthe order named, terminal means for said anode, grid, and cathode spacedaxially of said tube and connecting respectively said grid with saidintermediate conductor, said anode with one of the other of saidconductors and said cathode with the remaining one of said conductors,and a coupling between said transmis- 6 sion line sections formaintaining oscillations therein.

2. An oscillator comprising three telescoped conductors providingbetween them a pair of concentric cavity resonators, the telescopedextremities of the conductors being axially offset providing a stepwisearrangement regressive from the outer conductor toward the innerconductor, an electronic tube having anode and cathode terminals locatedat the respective ends of the tube and a grid terminal projecting froman intermediate portion of the tube, said tube interfitting with saidstepwise conductor arrangement with one of its said end terminals lyingclose to the extremity of the inner conductor and its grid terminallying close to the extremity of the intermediate conductor, meansproviding high frequency connections between the various terminals andthe various conductors, and feedback coupling between the two cavityresonators.

3. An oscillator comprising three telescoped conductors providingbetween them a pair of concentric cavity resonators, the telescopedextremities of the conductors being axially offset providing a stepwisearrangement which is regressive from the outer conductor toward theinner conductor, and an electronic tube having a cathode, a grid and ananode mounted in end-to-end relation in the order named, said tubeinterfitting with said stepwise conductor arrangement with its anodeterminal coupled with the inner conductor, its grid terminal with theintermediate conductor and its cathode terminal with the outerconductor, and a mutual coupling between said cavity resonators forsustaining operation of said tube as an oscillator.

4. An oscillator comprising three telescoped conductors defining betweenthem a pair of concentric transmission line sections, movable meansinterposed between the various conductors for determining the effectivelength of the said transmission line sections, means projecting from oneend of the said conductors for adjusting the said movable means and forthus tuning the transmission line sections, and a grid-controlledelectronic tube extending within the other end of said conductors, saidtube having its grid coupled to the intermediate conductor and its anodeand cathode respectively coupled to the inner and outer conductorswhereb oscillations may be developed upon proper tuning and feedbackadjustment of said transmission line sections,

5. An ultra high frequency device comprising three telescoped conductorsdefining between them a pair of concentric transmission line sections,movable means interposed between one pair of said conductors fordetermining the effective dimensions of the transmission line sectionbetween such conductors, means at one end of said conductors foradjusting the said movable means and thus tunin the said transmissionline section, said telescoped conductors terminating at the other end atdiiTerent axially displaced points to provide a stepwise arrangementprogressing from the inner to the outer conductor, and a gridcontrolledelectronic tube extending within the other end of said conductors, saidtube having terminals connected respectively with said anode, said grid,and said cathode and supported in axially spaced relation with theintermediate one of said terminals coupled to the intermediate conductorand the terminals connected with its anode and cathode respectivelycoupled to the other conductors, whereby oscillations may be developedupon proper relative tuning of said transmission line sections byadjustment of said movable means.

The following references are of record in the RICHARD C, JENSEN. JAMESE. KEISTER.

REFERENCES CITED file of this patent:

UNITED STATES PATENTS Number Name Date Samuel Aug. 15, 1939 Number

